| Industries such as nuclear and electroplating often generate wastewater containing toxic metals such as lead and organic ligands such as EDTA. Complexed aqueous metal species, such as Pb(II)-EDTA, are difficult to treat employing conventional metal removal methods. The present work investigated the adsorption and photocatalysis of lead-ligand complexes in TiO{dollar}sb2{dollar} suspensions.; Results from the Pb(II)-only and EDTA/NTA-only adsorption studies showed a cationic- and an anionic-type adsorption, respectively. Adsorption modeling results predicted similar trends. The 10{dollar}sp{lcub}-3{rcub}{dollar} and 10{dollar}sp{lcub}-4{rcub}{dollar} M Pb(II)-EDTA studies indicated an anionic-type Pb(II)-EDTA adsorption, i.e., Ti-EDTA-Pb{dollar}sp-{dollar}. However, the Pb(II)-NTA adsorption studies showed an increasing lead and decreasing NTA removal with an increase in pH. For the EDTA {dollar}>{dollar} Pb(II) studies, insignificant metal adsorption was noted between pH 2 and 10, whereas some EDTA adsorption occurred. Studies completed at Pb(II) {dollar}>{dollar} EDTA/NTA showed significant ligand adsorption even at high pH, which was not noted for the ligand-only adsorption studies. Additional surface species, i.e., Ti-O-Pb-EDTA{dollar}sp{lcub}3-{rcub}{dollar}, and Ti-O-Pb-NTA{dollar}sp{lcub}2-{rcub}{dollar}, were invoked to explain and successfully model such an enhanced ligand adsorption. These results indicate that adequate adsorption modeling of metal-ligand species needs to consider both anionic- and cationic-type surface complexation. Also, sub-surface transport modeling of such contaminants would also need to incorporate both surface species.; Pb(II)-EDTA photocatalysis was completed at several Pb(II)/EDTA concentrations and pH 4 to 6. 10{dollar}sp{lcub}-4{rcub}{dollar} M Pb(II)-EDTA photocatalysis studies showed complete complex destruction within 20-min, and 10{dollar}sp{lcub}-3{rcub}{dollar} M Pb(II)-EDTA systems within 1-hr. Acetate, formate, formaldehyde, ammonia, and nitrate were detected as reaction intermediates and products. CO{dollar}sb2{dollar} production was also noted. Results from stoichiometric studies showed no significant pH effects on Pb(II)-EDTA photocatalysis. However, Pb(II) {dollar}>{dollar} EDTA studies at pH 6 showed decreased CO{dollar}sb2{dollar} formation compared with the studies at pH 4 due to Pb(II) adsorption. Trends from the stoichiometric and non-stoichiometric studies indicated that Pb(II)-EDTA photocatalysis is both a surface and solution process. Generally, results from the present study indicate that TiO{dollar}sb2{dollar}-assisted photocatalysis can be employed to treat contaminated waters containing lead-ligand species. |
